Film-clad battery and method of producing a film-clad battery

ABSTRACT

A joint section where covering films  2   a   , 2   b  of film-covered battery  1  are heat-sealed together is formed with flat surface  6′  having thickness t 1  and groove  6  having thickness t 2 . Groove  6  serves to reduce the projection area of film-covered battery  1  by folding side  2   c  toward receiving section  2   a   1  with groove  6  serving as an edge, and groove  6  is made thinner than flat surface  6 ′ by Δt=t 1 -t 2 . Therefore, the length of covering films  2   a   , 2   b  produced on outer side  6   a  is shortened as compared with the case of folding the portion that has thickness t 1 .

This is a divisional application based upon U.S. patent application Ser.No. 10/574,562 filed Apr. 4, 2006, which is a National Stage ofInternational Application No. PCT/JP2004/014364 filed Sep. 30, 2004,claiming priority based on Japanese Patent Application No. 2003-348126filed Oct. 7, 2003, the contents of all of which are incorporated hereinby reference in their entirety.

TECHNICAL FIELD

The present invention relates to a film-covered battery which has abattery element encapsulated in a flexible materials used to cover thebattery, and a method of producing the film-covered battery.

BACKGROUND ART

In recent years, a reduction in weight and thickness has been strictlyrequired for batteries as a power supply for portable devices and thelike. Thus, in regard to materials used to cover the batteries, laminatefilms capable of a further reduction in weight and thickness have beenused more and more instead of conventional metal cans in which there isa limit to weight and thickness reductions. This laminate film which canbe freely formed into different shapes, compared with a metal can,comprises a thin metal film or a laminate of a thin metal film and aheat-seal resin film.

As a representative example of a laminate film used for materials usedto cover the batteries, there is a three-layer laminate film that has aheat-seal resin film, which is a heat seal layer, laminated on one sideof an aluminum thin film, which is a thin metal film, and a protectionfilm laminated on the other side.

Generally, in a film-covered battery which uses a laminate film for acovering material, a battery element comprising a positive electrode, anegative electrode, an electrolyte and the like is hermetically sealed(hereinafter simply called “sealed”) by covering the battery elementswith the covering material in such a manner that heat-seal resin film ispositioned inside, and by heat-sealing the covering material around thebattery element. Polyethylene or polypropylene, for example, is used forthe heat-seal resin film, while a nylon film or a polyethyleneterephthalate film, for example, is used for the protection film.

For reference, as a battery element, other than chemical batteries suchas a lithium battery, a nickel hydrogen battery and the like, thosehaving a charge accumulating function such as a capacitor also uselaminate film as a covering material.

In a film-covered battery, lead terminals are connected to a positiveelectrode and a negative electrode of a battery element, respectively,for leading the positive electrode and negative electrode to the outsideof the covering material to extend these lead terminals from thecovering material. The lead terminals are connected to the batteryelement by ultrasonic welding or the like before the battery element issealed. Also, the battery element is sealed by sandwiching the batteryelement with two sheets of covering material, and by heat-sealing thecovering materials along the peripheral edge. The covering materials areheat-sealed by first heat-sealing three sides of the covering materialsfor formation into a bag. Subsequently, air is exhausted from theinterior of the covering materials to produce a vacuum inside thecovering materials, the covering materials are brought into closecontact with the battery element by atmospheric pressure, and the oneside that remains is heat-sealed in this state.

When the battery element has a certain degree of thickness, the generalapproach is to form one of the covering materials into the shape of acollared container shape by deep-draw molding, such that the batteryelement is readily received therein, cover the covering material formedinto the container shape from above the battery element, and join thecollar by thermal fusing.

For preventing external moisture and the like from being introduced intothe film-covered battery and to prevent the electrolytic solution andthe like within the film-covered battery from escaping to the outside, athin metal film of aluminum or the like is used in the covering film asa barrier layer, but the heat-seal resin film layer is exposed along theedge of the joint section around the battery element, causing a leakpath based on the molecular transport phenomenon of the resin itself.Therefore, to improve the reliability of sealing for the film-coveredbattery, the leak can be reduced by increasing the width of the jointsection to extend the transmission path and to increase the resistance,however this causes the problem that a larger projection area of thefilm-covered battery. Thus, JP-A-2002-25514 proposes a reduction inprojection area by folding a joint section toward a battery elementreceiving section.

DISCLOSURE OF THE INVENTION

However, the foregoing folded joint section of the conventionalfilm-covered battery causes a problem of possible damage such as cracksthat open in the folded portion because of the inability of the outsidelayer to follow elongation of the film. This is because of the thicknessof the laminate film causes a difference in elongation between theinside and outside of the fold of the film. This phenomenon will bedescribed below with reference to FIGS. 1, 2, and 3.

For example, as illustrated in FIG. 1, film-covered battery 101 has ashape such that joint sections of two opposite sides are foldedsubstantially at right angles toward a battery element receiving sectionin order to reduce the projection area a projection area. As can be seenin a cross-sectional view near a joint section before foldingillustrated in FIG. 2, hardly any of protection film 102 c, thin metalfilm 102 d, and heat-seal resin film 102 e hardly vary in thickness inthe joint section.

However, as illustrated in FIG. 3, when this joint section is foldedfrom the bottom substantially at right angles toward the battery elementreceiving section, a layer on outer side 106 a of the fold is elongatedto become thinner, possibly causing a crack to appear. If a crack opensin thin metal film 102 d layer, a leak path is created through thecrack, and a short transmission path is formed from the crack to theinterior of the battery, resulting in possible damage to the performanceand to the reliability of film-covered battery 101.

To solve the foregoing problems, it is an object of the presentinvention to provide a film-covered battery which has a battery elementencapsulated in a flexible covering material, which is capable ofpreventing the covering material from damage that occurs when a jointsection is folded, and a method of producing the film-covered battery.

To achieve the above object, a film-covered battery of the presentinvention comprises battery elements having a configuration in which apositive electrode faces a negative electrode, and in which a coveringfilm having at least a heat-seal resin layer and a thin metal film layerare laminated, for encapsulating the battery element with the heat-sealresin layer being positioned inside, and for sealing the battery elementby heat-sealing a joint section having at least one folded side along aperipheral edge, and is characterized in that the joint section isformed with at least one fold, and the fold has a thickness smaller thana thickness of the joint section around the fold.

The film-covered battery of the present invention configured asdescribed above is formed with the fold having a smaller thickness inthe joint section. Specifically, since the fold has a smaller thickness,the outer side of the fold is not excessively elongated when the jointsection is folded along the fold. It is therefore possible to prevent acrack from appearing due to elongation of the covering films. Also,since the existence of the fold defines the folded position, the jointsection will not be folded at an inconvenient position. In this way, thefilm-covered battery after folding is readily made in uniformdimensions.

Also, in the film-covered battery, the fold may be a groove, or thegroove may be formed in at least one side of the joint section.

Also, in the film-covered battery, a plurality of the folds may beformed in the joint section, such that the joint section is folded alongeach of the folds.

A film-covered battery of the present invention comprises a batteryelement having a configuration in which a positive electrode faces anegative electrode, and in which a covering film having at least aheat-seal resin layer and a thin metal film layer are laminated, forencapsulating the battery element with the heat-seal resin layer beingpositioned inside, and for sealing the battery element by heat-sealing ajoint section having at least one folded side along a peripheral edge,and is characterized in that the joint section is formed with aplurality of folds, the folds have a thickness smaller than a thicknessof the joint section around the folds, the folds are grooves formed inat least one side of the joint section, and the joint section is foldedalong each of the folds.

Also, in the film-covered battery, the battery element may be one of achemical battery and a capacitor.

A fabrication method of a film covered battery of the present inventionis characterized in having a battery element encapsulated within acovering film that has at least one folder joint section formed aroundthe battery element, by comprising the steps forming at least one folderthinner than a thickness of the joint section therearound in the jointsection, and folding the joint section along the fold.

The film-covered battery of the present invention configured asdescribed above is formed with the fold having a smaller thickness inthe joint section. For this reason, the force required for folding isreduced. Also, since the existence of the fold defines the foldedposition, the joint section will not be folded at an inconvenientposition. In this way, the film-covered battery after folding is readilymade in uniform dimensions. Further, since the outer side of the fold isnot excessively elongated when the joint section is folded along thefold, a crack is unlikely to appear due to the elongation of thecovering films, thus making it possible to produce a reliablefilm-covered battery.

Also, the fabrication method of a film-covered battery may include thestep of forming the fold by pressing at least one side of the jointsection with a member having a protrusion, or may include the step ofheat-sealing and joining the joint section of the covering film having aheat-sealing property by heating and pressing the joint section with themember.

Also, the fabrication method of a film-covered battery may include thestep of preparing one of a chemical battery and a capacitor as thebattery element.

As described above, since the present invention forms a folded portionof the joint section of the covering films so that it is thinner, thefolding operation is facilitated. Also, since the elongation on theouter side is reduced when the joint section is folded, the coveringmaterial can be prevented from incurring damage. From the foregoing, thepresent invention can prevent a crack from opening in the middle of thejoint section to form a short transmission path into the interior of thebattery, and can also prevent the introduction of moisture and theescape of an electrolytic solution from accelerating, thus making itpossible to improve the performance and reliability of the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A perspective view of a conventional film-covered battery.

FIG. 2 A cross-sectional view of a joint section along the length a longside of the film-covered battery illustrated in FIG. 1 before it isfolded.

FIG. 3 A cross-sectional view of the joint section of the length longside of the film-covered battery illustrated in FIG. 1.

FIG. 4 A perspective view of a film-covered battery according to a firstembodiment of the present invention.

FIG. 5 An exploded perspective view of the film-covered batteryillustrated in FIG. 4.

FIG. 6 A perspective view illustrating the state of the film-coveredbattery illustrated in FIG. 4 before a joint section is folded.

FIG. 7 A cross-sectional view illustrating the state of the film-coveredbattery illustrated in FIG. 4 when the length a long side is connected.

FIG. 8 A cross-sectional view of the joint section along the length longside of the film-covered battery illustrated in FIG. 4 before it isfolded.

FIG. 9 A perspective view of the joint section along the length longsides of the film-covered battery illustrated in FIG. 4.

FIG. 10 A perspective view of a film-covered battery according to asecond embodiment of the present invention.

FIG. 11 A perspective view illustrating the state of the film-coveredbattery illustrated in FIG. 10 before a joint section is folded.

FIG. 12 An exploded perspective view of the film-covered batteryillustrated in FIG. 10.

FIG. 13 A perspective view of another film-covered battery according tothe second embodiment of the present invention.

FIG. 14 A perspective view illustrating the state of the film-coveredbattery illustrated in FIG. 13 before a joint section is folded.

FIG. 15 An exploded perspective view of the film-covered batteryillustrated in FIG. 13.

FIG. 16 A perspective view of a film-covered battery according to athird embodiment of the present invention.

FIG. 17 A perspective view illustrating the state of the film-coveredbattery illustrated in FIG. 16 before a joint section is folded.

FIG. 18 A perspective view of another film-covered battery according tothe third embodiment of the present invention.

FIG. 19 A perspective view illustrating the state of the film-coveredbattery illustrated in FIG. 18 before a joint section is folded.

FIG. 20 An exploded perspective view illustrating the configuration of abattery element in an example of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, embodiments of the present invention will be described withreference to the drawings.

First Embodiment

FIG. 4 is a perspective view illustrating the appearance of afilm-covered battery according to a first embodiment of the presentinvention, FIG. 5 is an exploded perspective view illustrating theconfiguration of the film-covered battery illustrated in FIG. 4, andFIG. 6 is a perspective view illustrating the state of the film-coveredbattery illustrated in FIG. 4 before a joint section is folded. In thisregard, FIG. 5 illustrates a film-covered battery which is not formedwith a groove that is a feature of the present invention.

As illustrated in FIG. 5, film-covered battery 1 of this embodimentcomprises laminate type battery element 5 (see FIG. 20) having positiveelectrode plates 8 and negative electrode plates 9 laminated throughseparators 10; rectangular covering films 2 a, 2 b for receiving batteryelement 5 together with an electrolytic solution; and positiveelectrode's lead terminal 3 and negative electrode's lead terminal 4connected to a positive electrode and a negative electrode of batteryelement 5, respectively.

As covering films 2 a, 2 b, known covering materials generally used forfilm-covered batteries can be used, such as laminate film which is madeof lamination of thin metal film and heat-seal resin. Covering films 2a, 2 b of this embodiment are made by laminating protection film 2 f,thin metal film 2 d, and heat-seal film 2 e (see FIG. 8).

Covering film 2 a is formed with receiving section 2 a 1 for receivingbattery element 5. Receiving section 2 a 1 may be formed, for example,by deep-draw molding. Battery element 5 is received in receiving section2 a 1 of covering material 2 a, and sealed by surrounding batteryelement 5 by sandwiching the same from above and from below togetherwith covering film 2 b, and by heat-sealing the peripheral edges ofthese covering films 2 a, 2 b. In this event, three sides of coveringfilm 2 a, 2 b are first heat-sealed for formation into a bag shape.After pouring electrolytic solution into bag-shaped covering films 2 a,2 b, air remaining therein is exhausted from the remaining open sides.Then, covering films 2 a, 2 b are hermetically sealed by heat-sealingthe remaining sides.

Covering films 2 a, 2 b are heat-sealed using thermal fusing head 7having protrusions 7 a and flat areas 7 b, shown in a cross-sectionalview in FIG. 7 when the joint section is heat-sealed. As illustrated inFIG. 7, thermal fusing head 7 sandwiches covering films 2 a, 2 b fromboth sides to heat seal them. FIG. 8 illustrates a partialcross-sectional view of the joint section after thermal fusing. Aportion heat-sealed by flat area 7 b is formed as flat surface 6′ havingthickness t₁, while a portion heat-sealed by protrusion 7 a is formed asgroove 6 having thickness t₂. In other words, the portion of groove 6 incovering film 2 a, 2 b is thinner than flat surface 6′ by Δt=t₁-t₂.Grooves 6 are formed in sides 2 c which are two opposing long sides fromwhich neither positive electrode lead terminal 3 nor negative electrodelead terminal 4 extend. These grooves 6 are folds along sides 2 c whichare folded toward receiving section 2 a 1 for reducing a projection areaof film-covered battery 1.

In the case of film-covered battery 1 of this embodiment, the forcerequired for folding is reduced by folding along groove 6 which isthinner than flat surface 6′ by Δt. Also, since the existence of groove6 defines the folded position, the joint section will not be folded atan inconvenient position. In this way, film-covered battery 1, after thefolding, is readily made in uniform dimensions.

Also, according to this embodiment, in addition to the effect ofimproving the workability in the foregoing manner, groove 6 hasthickness t₂ smaller than flat surface 6′ by Δt, so that elongation ofcovering films 2 a, 2 b on outer side 6 a can be reduced as comparedwith the covering films folded in the area having a thickness of t₁.Thus, this embodiment can prevent a crack from appearing due toexcessive elongation of outer side 6 a of the folded portion to improvethe reliability.

As described above, film covered battery 1 formed with grooves 6 alongsides 2 c of this embodiment can have improved folding workability, bein uniform dimensions, and have improved reliability as a film coveredbattery.

In this regard, while this embodiment has shown the configuration inwhich grooves 6 are formed along two opposing sides 2 c for folding thesame, groove 6 may be formed along one or more arbitrary sides. Also,groove 6 need not be formed over the entire length of the side, and maynot be formed, for example, in end regions of the side. Also, positiveelectrode lead terminal 3 and negative electrode's lead terminal 4 maybe extended from two or more different sides. Also, the joint sectionmay be folded in an arbitrary direction and at an arbitrary angle, suchas folded substantially at 180° on the side opposite to battery element5 receiving section. Also, while this embodiment has shown an example inwhich grooves 6 are formed by thermal fusing head 7 having protrusions 7a on both sides of side 2 c, groove 6 may be formed only on one side.

Second Embodiment

Next, a film-covered battery according to a second embodiment of thepresent invention will be described with reference to FIGS. 10 to 15. Inthis regard, since the film-covered battery of this embodiment issimilar in basic structure, groove forming method, and structure to thefilm-covered battery of the first embodiment, a detailed description isomitted.

While the first embodiment has shown a configuration in which thebattery element is encapsulated by two covering films, and sealed byheat-sealing the four sides therearound, film-covered batteries 11, 21of this embodiment have battery elements 15, 25 encapsulated in foldedsingle covering films 12, 22, and sealed by heat-sealing the threesurrounding sides.

In an example of FIGS. 10-12, groove 16 is formed along one sideopposing a side created by folding covering film 12, and a joint sectionthereof is folded toward receiving section 12 a 1 which receives batteryelement 15. FIG. 10 is a perspective view illustrating the appearance ofthe film-covered battery, FIG. 11 is a perspective view illustrating thestate of the film-covered battery illustrated in FIG. 10 before thejoint section is folded, and FIG. 12 is an exploded perspective viewillustrating the configuration of the film-covered battery illustratedin FIG. 10.

Film-covered battery 11 illustrated in FIGS. 10-12 has covering film 12folded along fold-over section 12′ of side 12 c′ adjacent to a side fromwhich positive lead terminal 13 and negative electrode lead terminal 14extend. This film-covered battery 11 has three sides other thanfold-over section 12′ connected by thermal fusing as illustrated in FIG.11, and groove 16 is formed only along side 12 c opposing fold-oversection 12′. The method for forming the groove and configuration ofgroove 16 are basically similar to the method shown in the firstembodiment. Film-covered battery 11 is also formed into film-coveredbattery 11 having only one side folded, illustrated in FIG. 10, byfolding side 12 c along groove 16 toward receiving section 12 a 1.

On the other hand, in the example of FIGS. 13-15, protrusions forpositive electrode lead terminal 23 and negative electrode lead terminal24 are provided on a side created by folding covering film 22 and on anopposing side, and grooves 26 are formed along the two other sides, andthese two other sides are folded. The remaining configuration is similarto the first embodiment, so that a description thereon is omitted. FIG.13 is a perspective view illustrating the appearance of the film-coveredbattery, FIG. 14 is a perspective view illustrating the state of thefilm-covered battery illustrated in FIG. 13 before the joint section isfolded, and FIG. 15 is an exploded perspective view illustrating theconfiguration of the film-covered battery illustrated in FIG. 13.

As illustrated in the exploded perspective view of FIG. 15, film-coveredbattery 21 illustrated in FIGS. 13-15 has covering film 22 folded alongfold-over section 22′ on side 22 c′ which opposes a side from whichpositive electrode's lead terminal 23 and negative electrode's leadterminal 24 extend. As illustrated in FIG. 14, film-covered battery 21has three sides connected by thermal fusing except for fold-over section22′. Then, grooves 26 are formed along this side 22 c′ and two sides 22c except for the side from which positive electrode's lead terminal 23and negative electrode's lead terminal 24 extend. The method for formingthe groove and configuration of grooves 26 are also basically similar tothe method shown in the first embodiment. A The Film-covered battery isalso formed into film-covered battery 21 which has two sides folded in amanner similar to film-covered battery 1 in the first embodiment, asillustrated in FIG. 13, by folding each side 22 c along groove 26 towardreceiving section 22 a 1.

Thus, like film-covered battery 1 in the first embodiment, film-coveredbatteries 11, 21 of this embodiment formed with grooves 16, 26 alongsides 12 c, 22 c can have improved folding workability and be made inuniform dimensions.

Also, film-covered batteries 11, 21 of this embodiment can reduceexposed sides of heat-seal resin film 22 e, which can be a leak path, byreceiving the battery element in single folded covering films 12, 22, ascompared with the battery element received using two covering films,thus making it possible to better prevent a degradation in performanceand reliability of film-covered batteries 11, 22 due to the introductionof external moisture and the escape of electrolytic solution.

Likewise, in this embodiment, the groove need not be formed over theentire length of the side, and may not be formed, for example, in endregions of the side. Also, the positive electrode's lead terminal andnegative electrode's lead terminal may be extended from two or moredifferent sides. Also, the joint section may be folded in an arbitrarydirection and at an arbitrary angle, such as folded substantially at180° on the side opposite to the battery element receiving section.Also, grooves 16, 26 may be formed on both sides or formed only on oneside.

Third Embodiment

Next, a film-covered battery according to a third embodiment of thepresent invention will be described with reference to FIGS. 16-19. Inthis regard, since the film-covered battery of this embodiment issimilar in basic structure, groove forming method, and structure to thefilm-covered battery of the first embodiment, a detailed description isomitted.

The film-covered battery according to the third embodiment of thepresent invention has a heat-sealed section of covering films folded aplurality of times to further reduce the projection area of thefilm-covered battery. FIGS. 16 and 17 illustrate an example in which twogrooves are formed along one side, while FIGS. 18 and 19 illustrate anexample in which three grooves are formed along one side.

FIG. 16 is a perspective view illustrating the appearance of thefilm-covered battery having two grooves formed along one side accordingto the third embodiment of the present invention, and FIG. 17 is aperspective view illustrating the state of the film-covered batteryillustrated in FIG. 16 before the joint section is folded.

As illustrated in FIG. 17, two grooves 36 a, 36 b are formedsubstantially in parallel along two sides 32 c from which neitherpositive electrode's lead terminal 33 nor negative electrode's leadterminal 34 is extended. Groove 36 a is provided for folding side 32 ctoward receiving section 32 a 1 in a manner similar to the respectiveembodiments described above. Groove 36 b formed outside of groove 36 ais provided for again folding over side 32 c which has been folded upalong groove 36 a which results in an edge. In other words, groove 36 bis located at the peak of side 32 c folded in a mountain shape. Sinceside 32 c is folded along grooves 36 a, 36 b, film-covered battery 31has a further reduced projection area.

On the other hand, FIG. 18 is a perspective view illustrating theappearance of a film-covered battery formed with three grooves along oneside, and FIG. 19 is a perspective view illustrating the state of thefilm-covered battery illustrated in FIG. 18 before the joint section isfolded.

As illustrated in FIG. 18, three grooves 46 a, 46 b, 46 c are formedsubstantially in parallel, respectively, along two sides 42 c from whichneither positive electrode's lead terminal 44 nor negative electrode'slead terminal 44 extend. Groove 46 a is provided for folding side 42 ctoward receiving section 42 a 1 in a manner similar to the respectiveembodiments described above. Grooves 46 b, 46 c formed outside ofgrooves 46 a, which are formed in close proximity to each other, areprovided for again folding over side 42 c which has been folded up alonggroove 46 a which results in an edge. Specifically, although side 42 cis folded in a mountain shape in this embodiment as well, side 43 c isfolded by nearly 90° at each of two locations along grooves 46 b, 46 c,instead of folding by nearly 180° at one location as in the exampleillustrated in FIGS. 16 and 17, thereby further reducing damage to thecovering films due to folding at an acute angle. Film-covered battery 41also has a further reduced projection area because side 42 c is foldedalong grooves 46 a, 46 b, 46 c.

Thus, film-covered batteries 31, 41 of this embodiment formed withgrooves 36 a, 36 b along side 32 c and grooves 46 a, 46 b, 46 c alongside 42 c can have improved the folding workability, be made in uniformdimensions, and have improved reliability as a film-covered battery,like film-covered battery 1 of the first embodiment.

Also, the film-covered batteries of this embodiment have further reducedprojection areas because the battery element is placed in covering films32, 42 which are folded in a mountain shape.

Likewise, in this embodiment, the groove need not be formed over theentire length of the side, but may not be formed, for example, in endregions of the side. Also, the positive electrode's lead terminal andnegative electrode's lead terminal may be extended from two or moredifferent sides. Also, the joint section may be folded on the sideopposite to the battery element receiving section, and the number offormed grooves may be three or more.

Also, in the respective embodiments described above, the fold has beenmade in a so-called groove shape, but the fold may be in any shape aslong as the thickness of the fold is smaller than the thickness of thejoint section other than the fold. For example, the fold may be in theshape of smooth concave.

Also, in the respective embodiments described above, the grooves on theouter side and inner side of the fold, shown as an example, havesubstantially the same groove shape, but the grooves are not so limited,and the groove on the outer side may have a different cross-sectionalshape from the groove on the inner side. For example, the groove on theouter side may have the bottom wider than that of the groove on theinner side, or vice versa. Also, while the respective embodiments haveshown the grooves in a concave shape on both sides as an example, thegrooves are not so limited, but only one of those on the outer side andinner side of the fold may be in a concave shape.

EXAMPLE

Next, a specific example of the present invention will be described withreference to the drawings used for describing the first embodiment,giving film-covered battery 1 in the aforementioned first embodiment asan example.

<Fabrication of Positive Electrodes>

In this example, lithium manganate powder having a spinel structure, amaterial which is carbonaceous and imparts electrical conductivity, andpolyvinylidene fluoride were mixed and dispersed in N-methyl-pyrolidone(represented by NMP in some cases) in a mass ratio of 90:5:5, andstirred into slurry. The amount of NMP was adjusted such that the slurrywould have a proper viscosity. This slurry was uniformly coated on oneside of an aluminum foil having a thickness of 20 μm, which would serveas positive electrode plate 8, using a doctor blade. The coating wasmade such that striped parts of a small region(in which the aluminumfoil exposed) were left uncoated. Next, the aluminum foil coated withthis slurry was dried in vacuum at 100° C. for two hours. Subsequently,the other side of the aluminum foil was also coated with the slurry in asimilar manner, and dried in a vacuum. In this event, the slurry wascoated such that the uncoated regions matched on the front and backsides.

The aluminum foil thus coated with an active material on both sides wasroll pressed. This was cut into rectangles, including the region notcoated with the active material, which were used as positive electrodeplates 8. The region which was not coated with active material was cutaway except for a portion thereof on one side which was left in arectangular shape, and the left portion was used as a tab.

<Fabrication of Negative Electrodes>

Amorphous carbon powder and polyvinylidene fluoride were mixed anddispersed in NMP in a mass ratio of 91:9, and stirred into slurry. Theamount of NMP was adjusted such that the slurry would have a properviscosity. This slurry was uniformly coated on one side of a copper foilhaving a thickness of 10 μm, which would serve as negative electrodeplate 6, using a doctor blade. The coating was made such that stripedparts of a small region(in which the acopper foil exposed) were leftuncoated. Next, the copper foil coated with this slurry was dried in avacuum at 100° C. for two hours. In this event, the thickness in whichthe active material had been coated was adjusted such that the logicalcapacity of negative electrode plate 9 per unit area and the logicalcapacity of positive electrode plate 8 per unit area was 1:1.Subsequently, the other side of the copper foil was also coated with theslurry in a similar manner, and dried in a vacuum.

The copper foil thus coated with an active material on both sides wasroll pressed. This was cut into rectangles whose vertical and horizontaldimensions were each 2 mm larger than those of positive electrode plates8, including the region not coated with the active material, which wasused as negative electrode plates 9. The region which was not coatedwith active material was cut away except for a portion thereof on oneside which was left in a rectangular shape, and the left portion wasused as a tab.

<Fabrication of Battery Element>

Positive electrode plates 8 and negative electrode plates 9 fabricatedin the foregoing manner, and separators 10 made of a micro-porous sheethaving a three-layered structure of polypropylene layer/polyethylenelayer/polypropylene layer were laminated one on another as illustratedin FIG. 20. In this event, negative electrode plate 9 was chosen for theoutermost electrode plate, and separator 10 was placed further outsidethis negative electrode plate 9 (in other words, they were laminated inthe order of separator/negative electrode plate/separator/positiveelectrode plate/separator/ . . . /negative electrode plate/separator).

Next, the tabs of positive electrode plates 8 and positive electrode'slead terminal 3 made of an aluminum plate with a thickness of 0.1 mmwere collectively ultrasonic-welded to make a charge collector with apositive electrode. Likewise, the tabs of negative electrode plates 9and negative electrode's lead terminal 4 made of a nickel plate with athickness of 0.1 mm were collectively ultrasonic-welded to make a chargecollector with a negative electrode.

<Sealing of Battery Element>

Two covering films 2 a, 2 b which are aluminum laminate films having afour-layered structure of nylon layer/aluminum layer/acid modifiedpolypropylene layer/polypropylene layer were used as covering materials.Covering film 2 a was formed with a recess whose size was slightlylarger than battery element 5 by deep-draw molding, such that coveringfilm 2 a is concave on polypropylene layer side, to create receivingsection 2 a 1.

Battery element 5 mentioned above was received by two covering films 2a, 2 b, laid one on top of the other, such that only positiveelectrode's lead terminal 3 and negative lead terminal 4 extended fromcovering films 2 a, 2 b, and three surrounding sides of covering films 2a, 2 b were connected by thermal fusing. The length of the two the twoopposing long sides adjacent to the side from which the lead terminalsextended were heat-sealed using a thermal fusing apparatus havingprotrusions on the surfaces of the fusing part of thermal fusing head 7,as illustrated in FIG. 7 to create a joint section having grooves 6illustrated in the perspective view of FIG. 6 and in the cross-sectionalview of FIG. 8.

Next, an electrolytic solution was poured into the interior of coveringfilms 2 a, 2 b, in which battery element 5 had been received, from theremaining sides which were not connected.

The electrolytic solution that was used was made up of 1 mol/liter ofLiPF₆ serving as a supporting electrolyte, and a mixed solvent ofpropylene carbonate and ethylene carbonate (mass ratio is 50:50). Afterthe electrolytic solution was poured, air remaining inside was exhaustedfrom the remaining open sides of covering films 2 a, 2 b, and batteryelement 5 was sealed by heat-sealing the remaining side.

Finally, the joint section was folded substantially at right anglestoward receiving section 2 a 1 such that groove 6 formed an edge, asillustrated in the cross-sectional view of FIG. 9, thereby fabricatingfilm-covered battery 1 which was a lithium secondary battery havingcovering materials made of a laminate film.

While the present invention has been described in connection withseveral representative embodiments and specific examples, it is apparentthat the present invention is not limited to them, and can be modifiedas appropriate within the scoop of the technical philosophy of thepresent invention.

For example, while a laminate film of a thin metal film and a heat-sealresin have been used as a flexible covering material, other materialscan also be used so long as they have a property that will adequatelyseal the battery element

Also, while the battery element that is used as an example is a laminatetype which has been used to alternatively laminate the positiveelectrode plates and the negative electrode plates, the presentinvention can also be applied to winding type element. Also while thebattery elements of a lithium secondary battery has been given as anexample to describe the battery elements, the present invention can beapplied to battery elements for other types of chemical batteries suchas a nickel hydrogen battery, a nickel cadmium battery, a lithium metalprimary battery or secondary battery, a lithium polymer battery and thelike, as well as a capacitor element and the like.

1. A fabrication method of a film-covered battery which has a batteryelement encapsulated within a covering film having at least one foldedjoint section formed around said battery element, said methodcharacterized by comprising the steps of: forming at least one foldthinner than the thickness of said joint section therearound in saidjoint section; and folding said joint section along said fold.
 2. Thefabrication method of a film-covered battery according to claim 1,comprising the step of forming said fold by pressing at least one sideof said joint section with a member having a protrusion.
 3. Thefabrication method of a film-covered battery according to claim 2,comprising the step of heat-sealing and joining said joint section ofsaid covering film having a heat-sealing property by heating andpressing said joint section with said member.
 4. The fabrication methodof a film-covered battery according to claim 1, comprising the step ofpreparing one of a chemical battery and a capacitor as said batteryelement.